Java中涉及布尔变量的无限while循环

Question

这是我的第一篇文章，如果我未能在本网站上遵循正确的格式/约定等，敬请见谅。我只编程了几个星期。

无论如何，我正在使用布尔变量和 while 循环编写一个基本的 Java 程序。该代码至少可以说非常“笨拙”，并且肯定可以变得更加优雅（尽管不是我有限的技能，所以再次道歉）。 如果布尔变量为真，则代码将正常运行。但是，如果变量为假，代码会进入一个 while 循环，即使输入了应该使语句为真的输入，循环也会继续进行。 知道是什么导致了这个无限循环。我几乎可以肯定这是基本的东西，但我似乎无法弄清楚。这是下面的代码。谢谢！

import java.util.Scanner;
import java.util.Random;
import static java.lang.System.out;
import static java.lang.System.in;

public class MB1 {
    public static void main(String args[]){
        char a, b, c, d;
        Scanner myScanner = new Scanner(in);
        boolean secondBoolean;

        out.println("Let's get started! Type in your 4-digit code:");
        a = myScanner.findWithinHorizon(".", 0).charAt(0);
        b = myScanner.findWithinHorizon(".", 0).charAt(0);
        c = myScanner.findWithinHorizon(".", 0).charAt(0);
        d = myScanner.findWithinHorizon(".", 0).charAt(0);

        secondBoolean = ((a == '1'|| a == '2'|| a == '3' || a == '4' || a == '5' || a == '6' || a == '7')
            && (b == '1' || b == '2'|| b == '3' || b == '4' || b == '5' || b == '6' || b == '7')
            && (c == '1' || c == '2'|| c == '3' || c == '4' || c == '5' || c == '6' || c == '7')
            && (d == '1' || d == '2'|| d == '3' || d == '4' || d == '5' || d == '6' || d == '7'));

            while (secondBoolean == false) {
            out.println("The code you typed is not valid. Please type a different code:");
            a = myScanner.findWithinHorizon(".", 0).charAt(0);
            b = myScanner.findWithinHorizon(".", 0).charAt(0);
            c = myScanner.findWithinHorizon(".", 0).charAt(0);
            d = myScanner.findWithinHorizon(".", 0).charAt(0);  
            out.print(a);out.print(b);out.print(c);out.print(d);
            } 
            if (secondBoolean == true){
                out.println('0');
            }
        }
    }

Answer 1

是的，当secondBoolean 为假时，您进入循环。 您将在此循环中循环，直到 secondBoolean 设置为 true，因此您必须在 while 循环中更新它。

另一方面，也许你的代码可以像这样整理一下；

List<String> nums = Arrays.asList("1", "2", "3", "4", "5", "6", "7");
secondBoolean=(nums.contains(a) && 
               nums.contains(b) && 
               nums.contains(c) && 
               nums.contains(d));

我只是自己开始java，但这看起来有点整洁！ 希望对您有所帮助。

Answer 2

您可以尝试仅将用户的输入读取为字符串并用“。”将其拆分

import java.util.Scanner;

import static java.lang.System.in;
import static java.lang.System.out;

public class MB1 {

    public static void main(String args[]) {
        char a, b, c, d;
        Scanner myScanner = new Scanner(in);
        boolean secondBoolean;

        out.println("Let's get started! Type in your 4-digit code:");
        String strIn = myScanner.nextLine();

        // Split input by "."
        String[] strAry = strIn.split("\\.");

        // create char array of equal length to String array
        char[] chrAry = new char[strAry.length];

        // convert strings to chars
        for (int i = 0; i < strAry.length; i++) {
            chrAry[i] = strAry[i].charAt(0);
        }

        // (unnecessary) assignment to a, b, c and d
        a = chrAry[0];
        b = chrAry[1];
        c = chrAry[2];
        d = chrAry[3];

        secondBoolean = ((a == '1' || a == '2' || a == '3' || a == '4' || a == '5' || a == '6' || a == '7')
                && (b == '1' || b == '2' || b == '3' || b == '4' || b == '5' || b == '6' || b == '7')
                && (c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7')
                && (d == '1' || d == '2' || d == '3' || d == '4' || d == '5' || d == '6' || d == '7'));

        while (!secondBoolean) {
            out.println("The code you typed is not valid. Please type a different code:");
            // ... read in code again. You possibly want to do this with a method
        }
        if (secondBoolean) {
            out.println('0');
        }
    }
}

Answer 3

secondBoolean 变量的值每次都必须重新计算。

替换

secondBoolean = ((a == '1'|| a == '2'|| a == '3' || a == '4' || a == '5' || a == '6' || a == '7')
        && (b == '1' || b == '2'|| b == '3' || b == '4' || b == '5' || b == '6' || b == '7')
        && (c == '1' || c == '2'|| c == '3' || c == '4' || c == '5' || c == '6' || c == '7')
        && (d == '1' || d == '2'|| d == '3' || d == '4' || d == '5' || d == '6' || d == '7'));

while (secondBoolean == false) {
    out.println("The code you typed is not valid. Please type a different code:");
    a = myScanner.findWithinHorizon(".", 0).charAt(0);
    b = myScanner.findWithinHorizon(".", 0).charAt(0);
    c = myScanner.findWithinHorizon(".", 0).charAt(0);
    d = myScanner.findWithinHorizon(".", 0).charAt(0);  
    out.print(a);out.print(b);out.print(c);out.print(d);
    } 
    if (secondBoolean == true){
        out.println('0');
    }
}

与

while (secondBoolean == false) {
    out.println("The code you typed is not valid. Please type a different code:");
    a = myScanner.findWithinHorizon(".", 0).charAt(0);
    b = myScanner.findWithinHorizon(".", 0).charAt(0);
    c = myScanner.findWithinHorizon(".", 0).charAt(0);
    d = myScanner.findWithinHorizon(".", 0).charAt(0); 

    out.print(a);out.print(b);out.print(c);out.print(d);

    secondBoolean = ((a == '1'|| a == '2'|| a == '3' || a == '4' || a == '5' || a == '6' || a == '7')
        && (b == '1' || b == '2'|| b == '3' || b == '4' || b == '5' || b == '6' || b == '7')
        && (c == '1' || c == '2'|| c == '3' || c == '4' || c == '5' || c == '6' || c == '7')
        && (d == '1' || d == '2'|| d == '3' || d == '4' || d == '5' || d == '6' || d == '7'));
    } 
    if (secondBoolean == true){
        out.println('0');
    }
}

您应该在循环的每次迭代中更新secondBoolean 的值。

---

此外，您可以通过替换代码来提高代码的可读性

String choices = "1234567";
secondBoolean = choices.contains(a + "") && choices.contains(b + "")
             && choices.contains(c + "") && choices.contains(d + "");

祝你好运

Answer 4

您处于无限循环中，因为您从未更改secondBoolean 的值。你应该在你的while循环中这样做。

另外，不要忘记在循环之前初始化你的 secondBoolean 变量（设置 secondBoolean = false，这样你的循环将至少运行一次）。